Comments by Laysence (Top 3 by date)

You could also use an excel library for C# which has a much better performances then usage of excel interop in C#, you can find the comparions sheet here.

You could try out this .NET's library Word documents, you would not go through your document line by line but instead you would read your Word files in C# and iterate through all its elements (Paragraphs, Tables, Pictures, etc.).